The present invention relates to a process for maintaining a constant tensile load on material during winding operations wherein the tensile load is kept constant by maintaining a constant material web speed during winding, and to a control arrangement suitable for use therein.
When processing material in web form it is frequently necessary for the web material to be temporarily wound onto a roll, before it can be further processed. A necessary condition for this is the maintenance of a constant tensile load thereon which, in general, can be achieved by providing a constant material web speed. In the paper and rolling mill industries, Ward-Leonard drives are customarily employed as control units for so-called hyperbolic winders in order to maintain a constant tensile load. The control units used therein are designed for large load drives and exhibit a high technical complexity. The high technical complexity and the large capital outlay characteristic of Ward-Leonard drives renders them undesirable for use with small load or power drives. Accordingly, there exists a great need in the art for a control system suitable for use with small load or power drives.
The winding of material in tape or wire form under a constant tensile load will be a process of constant power if the supply or web speed of the material is maintained constant. The change in the diameter of the winding of a roll as it picks up material will not change this relationship provided the web speed is maintained constant. It is true that, as the diameter of the winding becomes greater, the speed of the motor which drives the wind-up roll falls, however, at the same time its torque increases. Since the product of the drive motor's speed and torque gives its mechanical power, which corresponds to the tensile load on the material to be wound, and which remains essentially constant, a decrease in drive motor speed will not alter the tensile load if a constant web speed is maintained.